In one of the most recent and complete descriptions of the state of the art, in U.S. Pat. No. 4,427,362 it is stated that the essentially impossibility to achieve complete combustion combined with low NOx emissions except with a rather sophisticated high temperature multistage combustion process. Particularly low NOx emission levels are claimed not be achievable in "the initial combustion" (Col. 6, lines 65). Therefore it is stated necessary to have at least two oxidation stages, respectively multi zone or staged combustion.
These arrangements are expensive in many respects and do not provide easy retrofit potential in existing boilers, firing spaces inside existing boilers for example.
It is therefore a purpose of the present invention to dramatically reduce pollutants with simple means already and predominantly in the initial or first combustion stage. Other stages and combinations may be added.
The invention has particular application to methods and devices for reducing unwanted emissions, such as CO, HC, NO.sub.x and soot (carbon monoxide, hydro-carbons, nitrogen oxides and soot) in stationary furnaces and the like which use the assistance of air along with the fuel supply and at least one burning zone within the combustor, wherein the fuel may be liquid petroleum gas (LPG), or other burnable gases, fossil fuels, such as oil or coal and coal-based products or combinations thereof.
In the past such reduction of unwanted emissions have been done by recirculation of exhaust gases, by multi-stage combustion using additional burner assemblies, by flame division through the use of flame stabilizers by fuel conversion, and by catalysts used in the combustion process. These processes often involve great expense by necessitating the addition of expensive equipment to the furnace or combustor in which they are to be used. Further, such methods have often been used without the aid of a proper analysis of their effects on combustion, and so while eventually reducing unwanted pollutants they have sometime sacrificed combustion efficiency during the combustion process. Most of the proposed solutions have proved to have had such severe drawbacks that they could not realize their intended results and have thus far defined only a paper state of the art. A need therefore exists in which both high combustion efficiency and reduction of unwanted emissions can be achieved.